Steering by driving



July 1945. H. s. EBERHARD ETAL 2,379,623

STEERING BY DRIVING Filed Nov. 16, 1940 7 Sheets-Sheet 1 INVENTORJ Harmon J. Eberhard BY fiearqe W. Lew/5 ATTORNEY.

July 3, 1945. H. s. EBERHARD ETAL STEERING BY DRIVING 7 Sheets-Sheet 2 IN VENTORS Halrmon J. Eberhard Filed Nov. 16, 1940 BY fiearqe W. Lew/s M iXZy ATTORNEY.

July 3, 1945. H. s. EBERHARD ETAL STEERING BY DRIVING Filed Nov. 16, 1940 7 Sheets-Sheet 3 INVENTORS mon -S. fiber/24rd fieorge W. Lew/s M July 3, 1945. H. s. EBERHARD ETAL 2,379,628

STEERING BY DRIVING Filed NOV. 16, 1940 7 Sheets-Sheet 4 INVENTORS Harmon S. Eberhard BY Gearge W. Lew/5 ATTORNEY H. s. EBERHARD ETAL 2,379,628

July 3, 1945.

STEERING BY DRIVING Filed NOV. 16, 1940 7 Sheets-Sheet 6 July 1945 H. s. EBERHARD ETAL ,3

STEERING BY DRIVING 7 Sheets-Sheet 7 Filed Nov. 16, 1940 VMQ INVENTORS IZqrmonJf/bcrhard By car e GW/S ATTORNEY Patented July 3, 1945- STEERING BY DRIVING Harmon S. Eberhard, Peoria, 111., and George W.

Lewis, Cedar Rapids, Iowa, assignors to Caterpillar Tractor 00., San Leandro, 'Calif., a corporation of California Application November 16, 1940, Serial No. 365,980

(Cl. ISO-9.2)

8 Claims.

Our invention relates to steering by driving, and more particularly to the steering of vehicles, such as track-type tractors, by control of the drive to the traction means of such vehicles.

In self-propelled vehicles such as track-type tractors having an endless track at each side of the machine, steering is usually effected by control of the drive to each of such endless tracks by means of releasable drive establishing means in the form ofiiri ctiomsteeringclutehes. Such clutches generally comprise a driving member having spaced clutch discs or plates slidably secured thereto, and a driven member also having spaced clutch discs or plates slidably secured thereto and interposed between the clutch plates of the driving member. bination with a pressure plate acting against such clutch plates are provided for maintaining the clutch plates in tight frictional engagement to effect engagement of the clutch, so that th driving member may drive the driven member for transmission of a drive to the traction means. For disengaging the clutch and consequently releasing such drive, control means is associated with the spring means and the pressure plate to enable the pressure plate to be moved so as to reduce the pressure on such friction plates or apply a minimum or substantially no pressure thereon.

When a minimum or substantially no pressure is applied on the clutch plates, the drive is completely released, but by applying varying degrees of pressure on such clutch plates, less than the maximum amount at which such clutch plates are maintained in tight frictional engagement, slippage of the clutch obtains enabling partial transmission of the drive depending upon the extent of pressure applied. A associated with each of the tractionmeans, which may be applied when the associated steering clutch is disengaged. By the described m the vehicle may be turned sharply in one direction or the other when either one of the steering clutches is completely disengaged and the associated brake applied; and by slipping of either one of suclpsteeringrlatuhgstmignggpay be effected along a greater are depen ing upon the extent of such slipping.

In large size track-type tractors, the steering clutches are generally large; and consequently the spring pressure for holding the clutch plates together when the clutches are engaged is usually great. Since disengagement of the steering clutches is effected against action of the spring means for holding the clutch plates together, it

Spring means in comis apparent that where such spring pressure is great, it is sometimes quite burdensome for the operator to control steering of the machine, particularly under circumstances where he has to do a great deal of turning in a comparatively short time.

Our invention has as its objects, among others;-

the provision of improved hydraulic control j mechanism in association with steering clutches of the character described, which will facilitate the work of the operator of the machine in steer- 1 ing the machine; enable the same type of operation that obtains with respect to manually operable mechanical mechanism, but much easier; enable manual operation of the steering clutches in case of failure of the hydraulic control mechanism or lack of hydraulic power; and which has a common pumping means therefor. Other objects of our invention will become apparent from a perusal of the following description thereof.

Referring to the drawings:

Fig. 1 is a more or less schematic side elevational view of a track-type tractor with a portion thereof broken away to illustrate the general arrangement of our hydraulic steering clutch control mechanism.

Fig. 2 is a rear elevational View of the tractor of Fig. 1, with parts shown broken away and parts omitted from the View, to illustrate the arrangement of the steering clutches.

Fig. 3 is a sectional elevation of the steering clutches, taken in a plane indicated by line 3-3 in Fig. 2.

Fig. 4 is a horizontal sectional view of the hydraulic control mechanism, taken in a plane indicated by line 44 in Fig, 1.

Fig. 5 is a vertical sectional view of the hydraulic control mechanism taken in planes indicated by line 5-5 in Fig. 4.

Fig. 6 is a transverse sectional view taken in a plane indicated by line 66 in Fig. 5.

Fig. 7 is a transverse sectional view taken in a plane indicated by line 'l! in Fig. 5.

Fig. 8 is a horizontal sectional view taken in a plane indicated by line 8-8 in Fig. 6*.

Fig. 9 is an enlarged fragmentary horizontal sectional view of the valve control mechanism forming part of the hydraulic control mechanism appearing in Fig. 4; the parts in Fig. 9 being illustrated in neutral position.

Fig. 10 is a view similar to Fig. 9 illustrating one of the valve control members in a position where the associated steering clutch is partially disengaged.

For purposes of illustration, the mechanism of our invention is shown embodied in a tracktype tractor where it is particularly adapted. However, it is equally applicable in any type of vehicle where steering is effected by control of drive establishing means to associated traction means. With reference to Figs. 1, 2 and 3, which illustrate the general arrangement of the steering clutches, such tractor comprises a tractor body including engine 2 and operators station 3. At each side of the tractor body, is an endless track mechanism including endless track 4, front idler 6, and final drive sprocket 1 supported upon a truck frame a portion 8 of which is shown in Fig. 2. As is usual in track-type tractors, the endless track mechanisms are connected to oscillate or pivot about the axis of final drive sprockets l; and such final drive sprockets engage the endless tracks 4 for propulsion of the machine.

Driving of final drive sprockets l is from cross shaft 9 journalled in spaced walls H in case l2, which walls I I form a so-called wet compartment I3 containing lubricant, and also a bevel gear l4 secured to cross shaft 9 and meshing with a bevel pinion (not shown) by which the drive is transmitted from the engine to bevel gear 14 and consequently the cross shaft. At the outer side of each of walls H is formed a so-called dry compartment [6 which does not contain lubricant, but in which is located a friction steering clutch l1 adapted to transmit a drive from the cross shaft 9 to the associated sprocket I through final drive gearing l8,

The friction steering clutches may be of any suitable construction; and reference is made to Best Patent No. 1,501,740, dated July 15, 1924, as illustrating a form of multiple disc steering clutch substantially the same in principle as that disclosed herein. Each of such steering clutches comprises an outer driven drum l9 connected to final drive gearing l6, and an inner driving member 2| secured to an end of cross shaft 9 for rotation therewith and having an outer radially extending peripheral flange 23. Secured for rotation with driven drum I9 but axially slidable therein in suitable keyways 24 are spaced friction discs or plates 26; and complementary spaced friction discs or plates 21, secured for rotation with driving member 2| but axially slidable in suitable keyways 28, are interposed between the driven friction plates 26. When all of such friction plates 26 and 2'! are tightly pressed together, it is apparent that each clutch will be engaged to transmit a drive therethrough from cross shaft 9 to the associated final drive gearing 3.

Spring means is provided for normally maintaining the friction plates of each clutch in tight frictional engagement so that the clutch may be engaged. The driving member 2| has a plurality of pins 2-9 extending axially therethrough and slidable therein. At its outer end, each pin is provided with a head 3| which provides an abutment fora spring 32 compressed between such head 3| and the outer side of driving member 2!. The inner end of each pin 29 is also provided with a head 33 which provides an abutment for pressure plate 34 bearing against the friction plates at one side; while the other side of such friction plates bears against peripheral flange 23. Pressure plate 34 is journalled freely about cross shaft 9 and is axially slidable along it; and by virtue of the action of springs 32, it is apparent that it will be normally thrust outwardly so as to maintain the friction plates 26 and 21 in tight frictional engagement for establishment of the drive through the clutch. Inward movement of the pressure plate results in reduction of pressure on the friction plates; and depending upon the extent of such inward movement, the clutch may be completely disengaged, or partially disengaged to provide slippage thereof. In this connection, a brake 35, controllable by suitable control means (not shown) at operators station 3, is associated with each driven drum I 9, to brake the associated traction means when the clutch is disengaged to produce sharp turning of the vehicle.

Control mechanism is provided, actuatable through manually manipulatable steering clutch control levers 36 at the operators station 3, for moving each of pressure plates 34 inwardly against the action of springs 32. Such control mechanism comprises a collar 31 journalled about the hub 38 of each pressure plate 34 through a suitable bearing 39, and which engages a side of such hearing by means of an outer flange 4| so as to efiect inward movement of the pressure plate when the collar is moved inwardly. Inward movement of collar 31 is effected by means of levers 42 which engage at one end lugs 43 formed on the periphery of collar 31 and which are pivoted intermediate their ends on an upright shaft 44 secured in brackets 46 fixed to case [2. At the ends opposite those which engage lugs 43, levers 42 are connected through an upright connecting member 41 which has a pin 48 adjustably secured therein. The inner end of each pin 48 is formed with a ball head 49 engaging in complementary shaped socket 5| secured to the lower end of rotatably mounted upright shaft 52; the upper end of such shaft having connected thereto a lever 53 which at its inner end is provided with a roller 54 engaging actuating mechanism 56 in which the hydraulic control mechanism of my invention is interposed, and which is adapted to be moved rearwardly by the associated steering clutch control lever 36. The direction arrows in Figs. 2 and 3 illustrate how the described disengagement of the steering clutches is eifected by movement of the steering clutch control levers.

When such actuating mechanism 56 is solely a mechanical linkage connection from each lever 53 to the associated clutch control lever 36, it is apparent that if clutch springs 32 exert comparatively high pressure on the clutch plates, as is the case in large size tractors, much effort is required on the part of the operator in hand manipulating the clutches against the action of such springs. As was previously mentioned, our invention is designed to obviate this difficulty by the employment of hydraulic control mechanism which provides power operable means for controlling the clutches, Such power operable hydraulic mechanism is controllable through control levers 36, and is designed to provide substantially the same action on the steering clutches as would obtain by hand manipulation of the steering clutches, except much easier.

With reference to Figs. 4 through 8, the power operable hydraulic control mechanism includes common pumping means for a plurality of actuating means, to provide for simplicity of construction. It is contained in a valve housing 6| attached to the top of case I 2 and a pump housing 62 projecting through aperture 63 in the top of case l2 and secured to the underside of valve housing 6|. A single pump 62 in pump housing 62 is driven from engine 2 through transmission shaft 64 extending from the speed change transmission 66 and which rotates continuously while the engine is running and the master clutch is engaged; such shaft 64 being connected to rotate gear 61 secured to pump driving shaft 68 journalled in and extending into pump housing 62. If so desired, pump 62' may be driven continuously even when the master clutch is disengaged by providing a direct connection thereof with the engine ahead of the master clutch.

The pump 62 in pump housing 62 may be of any a e construction capable of maintaining a suitable pressure flow of fluid, such as oil, through valve housing 6 I. We preferably employ a substantially constant volumetric discharge rotary gear pump which comprises driving gear 69 integral with shaft II which is secured by collar I2 to driving shaft 68. Gear 69 is located in pump compartment I3 formed in a cap I4 detachably secured by means of cap screws I6 to a vertical wall II of pump housing 62. A driven pump gear 19 meshes with driving pump gear 69; and both of such gears are enclosed by block BI held against vertical wall II by bearing cap 82 secured by cap screws 83; such bearing cap 82 providing journal means for a stub shaft 84 forming an integral part of each of gears 69 and I9 at one side thereof; while at the opposite side of such gears, vertical wall 11 provides journal means for a stub shaft 85 of gear I9 and shaft 'II of gear 69. Pump gears 69 and I9 are thus enclosed in a fluid tight compartment 86 into which a suitable hydraulic medium, such as oil, is drawn and from which such medium is discharged, by rotation of the gears.

Oil is contained in a reservoir 81 in pump housing 62 and is sucked into pump compartment 86 through passage 88 in vertical wall I1, filter element 89 in wall 11, upright passage 9| also in wall 11., and port 92 communicating with passage 9I and with the suction side of the pump gears 69 and I9. The oil under pressure from the discharge side of the pump gears, is discharged through port 93 in wall I! and which communicates with upright discharge passage 94 extending through wall 11 and from pump housing 62 into valve housing 6|; the junction between valve housing 6| and pump housing 62 being leak proofed by means of gasket 96, and by a packing sleeve 91 within the adjacent portions of passage 94 at such junction. The oil under pressure effected by the pump 62' flows through valve housing 6| in a manner to be subsequently described;

and from such valve housing, it flows back into reservoir 81 through cooperating apertures 98 formed in the adjacent walls of valve housing BI and pump housing 62. Thus, the pump maintains a continuous flow of oil under substantially constant pressure. of oil from time to time when needed, we provide a filler spout 99 in the top wall of valve housing 6|, and which communicates with filter element IIII in valve housing 6 I. From filter element IIJI the oil can flow into reservoir 81 through the apertures 98.

A plurality of control valves, each associated with an actuating piston, are provided in valve housing 6| to control the flow of oil pumped by the common pump 62, and actuate levers 53 against the load of clutch springs 32. As is illustrated in Fig, 4, such levers 53, which are connected to upright shafts 52, are enclosed in valve housing 6| and the rollers 54 thereon engage substantially cup-shaped actuating pistons III, the movements of which are controlled through the associated valve mechanism. The hydraulic control and actuating means associated with each steering clutch is the same; hence, in the subse- For replenishing the supply quent description of such means, reference will be made primarily to only one of them.

With reference to Figs. 4, 6 and 9, the hydraulic power control mechanism is mounted in stationary body means which includes a pair of stationary hollow sleeves II2 press fitted in wall II3 of valve housing 6|. Each of these sleeves is provided with a rear annular groove II4, an intermediate annular groove H6 and a front annular groove I I1, all of which communicate with the interior of such sleeve through radially extending ports or apertures H8. The rear end of each sleeve II2 projects beyond wall H3; and it is upon such projecting end that piston III is adapted to slide axially. Valve control mechanism is axially slidable within each of stationary sleeves II2 comprising a hollow valve member I I9 having interior passage I2I formed in its rear end. For convenience in manufacture, such valve member H9 is made of a front part I22 removably press-fitted on rear part I23; and it is adapted to be thrust forwardly by means of spring I24 interposed between shoulder I26 on valve member I I9 and the inside of the rear end I26 of movable piston I I I. The steering clutch springs 32 in each clutch serve to thrust the associated lever 53 forwardly, and exert greater pressure than spring I24.

As a result, when the associated clutch is engaged, piston I I I provides an abutment for spring I24, and valve member I I9 is thrust forwardly by such spring I24 against a rod I25 slidably mounted in a boss I25 formed integral with valve housing 6|. Rod I25 is thrust forwardly by a spring I21 interposed between packing gland I21 and socket member I28 formed at the forward end of such rod I25. Such socket member I28 engages linkage I28 which is adjustable as to length at I29, and which is pivotally connected to an associated clutch con-trol lever 36. A suitable flexible sealing boot I29 is provided between linkage I28 and boss I25; while socket member I28 is formed with suitable bleed apertures I30. Rearward movement of rod I25 is limited to the proper extent by means of a stop I38 formed as a shoulder within boss I25 and which is adapted tgsbe engaged by the rear end of socket member The described connection between a lever 53 and an associated manually manipulatable clutch control lever 36, including linkage I28, rod I25, valve member I I9 and piston I I I, provides axially movable mechanical means whereby upon rearward movement of the associated clutch control lever 36, the associated steering clutch may be disengaged. This is so because without the action of hydraulic pressure created by the common pump 62', rearward movement of valve member II9 as effected by the associated clutch control lever 36, will cause it to bear against rear end I26 of piston III, and consequently urge lever 53 rearwardly against the action of the associated steering clutch springs 32. In this connection, the piston II I and associated valve member form part of the hydraulic actuating means as will be more fully described hereinafter; and since these elements are adapted to provide part of solely manually controllable clutch disengaging mechanism, it is seen that the hydraulic actuating mechanism embodies means enabling manual control of the clutches upon lack or failure of hydraulic power, which is an important feature of our invention.

Adjacent the solid forward portion of valve member H9 is formed an elongated peripheral groove I3I which in the neutral position of the hydraulic control mechanism i. e., when the associated steering clutch is completely engaged, communicates with the apertures H9 communicating with intermediate groove H6 and front groove H1 in stationary sleeve I I2. At the rear of such groove I3I and communicating with inte rior passage I2I of valve member H9 are a plurality of radially extending apertures or ports I32 which in the neutral position of valve member II 9 are closed by the portion I33 of stationary sleeve H2, intermediate rear groove II4 intermediate groove II6. However, when valve member H9 is moved rearwardly to disengage the associated steering clutch, apertures I32 communicate with an annular groove I34 formed in the inner wall of stationary sleeve I I2, and which in turn communicates with rear groove H4 through the associated apertures H8. Thus, apertures I32 form inlet ports for flow of fluid into valve member H9.

A spring pressed hollow check valve I36, the function of which will be subsequently described, is mounted within valve member H9 in passage I2I, and is adapted to seat against a shoulder I31 formed rearwardly of but adjacent inlet. ports I32. A spring I38 bearing against such check, valve I36, is adapted to maintain the valve closed, but upon flow of fluid under pressure through inlet ports I32, the valve will become unseated against the action of spring I38, and fluid will flow into passage I2I through substantially radially extending ports I39 formed in the check valve rearwardly of its seat. The rear end I 46 of valve member H9 is closed, but adjacent such end are formed radially extending discharge ports I4I to allow fluid under pressure to escape from valve passage I2I and act against the rear end wall I26 of piston III, past which such fluid can escape through bleed apertures or ports I42 formed in such piston end wall I26, and which communicate with a central port I43. End I40 of valve member H9 is tapered and the wall of aperture I43 has a complementary taper whereby upon rearward movement of valve member II 9, end I40 serves as a valve tending to close port I43. The function of discharge ports MI in valve member H9, bleed ports I 42 in piston III, and the relationship of port I43 with respect to ports MI and valve end I40, will be subsequently explained.

Wall H3 is provided with passages, which in cooperation with grooves H4, H6 and H1, and apertures H8, form a continuous passageway in the body means including sleeves H2 and wall I I3, for flow of oil therethrough. Such passages include passage II between sleeves H2, and which communicates with passage 94 through which fluid is discharged by pump 62, and also with the rear grooves H4 in sleeves H2. Adjacent the left side of the left hand sleeve I I2 and communicating with rear groove I I4 in such left hand sleeve I I2 is a second passage I52 which in manufacture is drilled in line with passage I5I and is subsequently sealed at its outer end by plug I53. Adjacent passage I 52 and in front thereof is an intermediate passage I54 communicating with intermediate groove H6 in the left hand sleeve H2; such passage I54 being sealed at its outer end by sealing plug I56. Communication is provided between passages I52 and I54 by an aperture I51 which may be conveniently formed by drilling through the underside of wall H3 at the proper location and subsequently sealing the lower end of such aperture I51 by sealing plug I58.

In effect, passages I52 and I54, and aperture I51 form a single passage establishing communication at the left side of grooves H4 and H6 in the left hand sleeve H2. Between sleeves H2 and communicating with front groove H1 of left hand sleeve H2 is a passage I59 which is conveniently formed by drilling during which is formed a dummy passage I6I subsequently sealed by plug I62. Plugs I53, I56 and I62 are held sealed by plate I63 secured to the left side of valve housing 6I by cap screws I64. Passage I59 communicates through an aperture I66 formed similar to aperture I51, with a passage I61 which in turn communicates with the intermediate groove H6 in the right hand sleeve II 2; aperture I66 being sealed by sealing plug I68. Thus, passage I59, aperture I66 and passage I61 form a single passage establishing communication between the front groove H1 of left hand sleeve I I2 and the intermediate groove I I6 in right hand sleeve II 2. Passage I61 may be conveniently formed by drilling; and in such drilling a dummy passage I 69 is formed, which is subsequently sealed by sealing plug I1I. At the right hand side of the right hand sleeve I I2 is formed a discharge passage I12 which communicates with front groove H1 in such right hand sleeve and with reservoir 81 in valve housing 6I.

In operation, when the tractor is moving and both steering clutches are fully engaged so that the tractor will travel straight ahead, the clutch springs 32, valve member springs I24 and check valve springs I38 will cause the parts of the hydraulic control mechanism to assume the neutral position illustrated in Fig. 9. As previously explained, pump 62' will continuously pump fluid under pressure; but, in such neutral position, the pumped fluid has no effect on actuating pistons I I I because it is bled back into pump reservoir 81 after passage through the valve housing 6| in the following manner. From inlet passage 94, fluid fills passage I5I, the rear grooves II 4 in sleeves H2, apertures H8 communicating with such grooves, and also annular grooves I34 formed in the inner walls of sleeves I I2. In such neutral position of the parts, escape of fluid is blocked at the right hand side of passage I5I.

From rear groove H4 in left hand sleeve H2, fluid fills and flows through the passage formed by the passage I52, aperture I51 and passage I54; intermediate groove I I6 in left hand sleeve I I2 and the associated apertures II 8; and annular groove I3I in left hand valve member H9. Fluid can not escape through dummy passage I6I because it is blocked by plug I62, as was previously explained. Next, fluid flows from groove I3I in left hand valve member H9 through apertures H8 associated with front groove H1 in the left hand sleeve H2, and fills the passage formed by passage I59, aperture I66 and passage I61, From passage I61, fluid flows around and fills intermediate groove H6 in right hand sleeve H2, and flows through the associated apertures H8 to fill groove I3I in the right hand valve member H9. Fluid flowing into passage I69 can not escape because such passage is plugged by plug I1l, as was previously related. From groove I 3I in right hand valve member H9, fluid flows out through discharge passage I12 into the valve housint from which it flows through the cooperating apertures 98 in the valve housing and in the pump housing, into pump housing reservoir 81 from which it is recirculated by pump 62'.

From the preceding, it is seen that in the neutral position of the parts, the fluid pumped continuously through the described tortuous passageway in the stationary body means formed by sleeves H2 and wall H3, is bled back into the pump housing. Consequently, no pressure can be exerted on actuating pistons III to actuate them against the load of clutch springs 32 and the clutches will remain engaged. In order to have the pressure of the pumped fluid actuate either or both of pistons III to disengage the clutches, it is necessary that escape of fluid back into the pump housing be blocked. This is accomplished by movement of either one or both of valve members I I9 rearwardly from their neutral positions, and which when so moved close one portion of the passageway for flow of fluid through the body means and establish communication of inlet ports I32 with another portion of suchpassageway.

For example, to initiate disengagement of the right hand steering clutch and have it remain disengaged with only a slight degree of slippage so that the tractor will turn to the right alon a big are when it, for example, is traveling on level ground or uphill, the right hand valve member H9 must be moved rearwardly through the as ciated clutch control lever 36 to the position where it just shuts off the apertures I I8 communicating with front groove II! in right hand sleeve I I2 so as to shut off passage I12 and block escape of fluid back into the pump housing. In this connection, during the described rearward movement of the right hand valve member II9, end I40 of such valve member serves as a valve which reduces the effective area or the annular passage formed between port I43 and end I40. Inlet ports I32 in such right hand valve member III! are so spaced that in the related position, they communicate with groove I34 in right hand sleeve II2. In Fig. 9, we have shown in phantom lines the position which some of the parts assume when right hand valve member H9 is moved just to shut off discharge passage I12 and uncover inlet ports I32 in such right hand valve member.

In such position, fluid will flow from passage 94 around right hand valve member H9, in the mannerpreviously described, but even though passage I12 is shut oil, pressure of fluid will not act against left hand piston III because the inlet ports I32 in left hand valve member II9 are not uncovered. However, since inlet ports I32 in right hand valve member II9 are uncovered, pressure of fluid flowing through passage 94 will act to move right hand piston III in the following manner. From passage 94, fluid will flow through passage II around rear groove H4 in right hand sleeve II2, through the associated apertures H8 and into annular groove I34 in right hand sleeve II2. From such annular groove I34, fluid flows through inlet ports I32 in right hand valve member II9, which ports have been uncovered in the manner already related. As a result, the pressure of the fluid will act against check valve I36 to effect unseating of check valve I36 against the action of spring I38 Fluid flowing past unseated right hand check valve I36 passes through ports I39 in such valve, continues its flow through passage I2I in right hand valve member I I3 and escapes out through discharge ports I4I to act against the rear end I26 of right hand piston III to thrust it rearwardly against the load of clutch springs 32 by virtue of the pressure which is built up against right hand piston III from rearward movement of valve member end I40 which results in reduction of the effective area of port I43. In this connection, fluid will escape back into valve housing 6-I through piston bleed port I43; and hence when rearward movement of valve member H0 is stopped in the described position, further rearward movement of piston member IIIwill also crease by virtue of such bleeding. However, the piston will remain in a relatively stationary position against the clutch spring load because port I43 and valve member end I40, the clutch spring load, and the pump pressure, are all so correlated as to provide an escape passage through port I 43 which bleeds less pressure than that created by the pump.

Now, should right hand valve member H9 be moved further to the rear from the phantom line position shown in Fig. 9, by further rearward movement of the associated clutch control lever 36, the rear end I40 of such valve member gradiently reduces further the effective area of the annular passage between the wall of port I43 and end I40. This causes gradiently less pressure to bleed out through such piston port I43; and the pressure builds up within piston III to actuate it rearwardly against the associated clutch springs 32 and effect further disengagement of the clutch against the increasing load offered by such clutch springs as they become gradiently compressed. The increasing load offered by the clutch springs as they become compressed always balances the increasing pressure built up against piston III by virtue of the decreasing effective area through port I 43. Hence, when such further rearward movement of the associated clutch control lever 36 is terminated, piston III will assume a substantially stationary position against the load of the associated clutch springs 32, and the clutch will remain disengaged, to an extent which is determined by the extent of movement of the associated clutch control lever 36. In Fig. 10, the right hand clutch control mechanism is shown substantially fully disengaged. The fully disengaged position of the clutch is determined by stop I30.

From the preceding, it is seen that the valve member I I9 and its discharge ports in cooperation with the bleed ports I42 in piston III, provide means in the hydraulic power actuating mechanism, enabling complete disengagement of the associated steering clutch or any degree of partial disengagement thereof, depending on the extent of movement of the associated valve member II9 as determined by the extent of movemerit of the associated steering clutch control lever 36; and when such valve member H9 is moved from its neutral position, the extent of movement of the associated piston III will be a function of the extent of movement of the valve member. Hence, the steering clutch may be manipulated to provide all degrees of slippage thereof, or complete disengagement, in the same manner that exists with heretofore employed strictly manual controls for steering clutches, so as to enable delicate maneuvering of the vehicle. This is an important feature of the invention because if the hydraulic actuating mechanism were of the type that caused a clutch to be either fully engaged or fully disengaged with no intermediate degrees of slippage, it would be extremely difficult to make satisfactory smooth turns.

Manipulation of the left hand control mechanism is identical to that already described with respect to the right hand control mechanism, and occurs when left hand valve member H9 is moved rearwardly by the associated clutch conto the positions where their inlet ports I32 are uncovered to admit fluid pressure against both \pistons at the same time. In this connection, the described hydraulic actuating mechanism, 1 ill enable disengagement of either one of the steering clutches to an extent greater than the father, depending upon the extent that either of c'pntrol levers 36 is moved rearwardly.

l Check valves I36, in cooperation with the ends I, of valve members H9 adapted to close ports I43, perform the important function of precluding kickback of either one of clutch control levers 36 which may have been moved to a position where the associated steering clutch is disengaged or partially disengaged, when the other steering clutch control lever 36 is moved rearwardly to disengage or partially disengage the other steering clutch. Reference is made to Fig. 10 for a more detailed explanation. For example, with the right hand steering clutch substantially disengaged and the left hand steering clutch fully engaged, it will be observed that if left hand valve member I I9 were moved rearwardly so as to cause disengagement of the associated steering clutch, with consequent bleeding of fluid through the left hand piston ports I42, communication would be established between the bleed ports I42 of both pistons through the previously described passageway in body means H2 and H3.

At the moment when bleeding occurred through bleed ports I42 in the left hand piston III, fluid pressure within right hand piston I I I would momentarily become less by virtue of such communication between the sets of piston bleed ports. Without the right hand check valve I36, this would cause the load effected by the springs 32 of the associated right hand steering clutch to kick back the entire right hand mechanism including the right hand clutch control lever 36, which might result in injury to the operators hand. However, this action can not occur because as soon as the pressure in right hand piston III tends to become less, the right hand check valve I36 will seat, and the clutch spring load will cause the right hand piston discharge port I43 to become closed by tapered valve end I40 to preclude further bleeding of fluid. Thus, fluid under pressure will be trapped within right hand piston III to preclude the kickback. As soon as the pressure in left hand piston III balances the pressure in right hand piston HI, then the right hand check valve I36 will reopen.

As was previously related, should leakage occur in the valve housing, or should the hydraulic D wer fail from any other cause, the steering clutches may be operated entirely by manual power, because under such circumstance the rear end I40 of each of valve members H9 may be moved by rearward movement of the associated steering clutch control lever 36 to abut the end wall I26 of the associated piston III, and thereby move the associated lever 53 for disengagement of the associated steering clutch.

We claim:

1. In a vehicle having drivable traction means at each side thereof; a friction steering clutch interposed in the drive to each of said traction means to enable steering of said vehicle by control thereof; and hydraulic mechanism for controlling said steering clutches including a manually manipulatable control member associated with each of said clutches, and hydraulic actuating means interposed between each of said control members and the clutch associated therewith, each of said actuating means embodying means enabling manual control of the associated clutch by manipulation of the associated control member upon lack of hydraulic power.

2. In a track-type tractor having drivable endless track mechanism at each side thereof; an engine for driving said endless track mechanisms; a friction steering clutch interposed in the drive to each of said endless track mechanisms to enable steering of said tractor by control thereof; and hydraulic mechanism for controlling said steering clutches independently or together including a manually manipulatable control member independently associated with each of said clutches, hydraulic actuating means interposed between each of said control members and the clutch associated therewith, and common pumping means for said actuating means driven from said engine, each of said actuating means embodying means enabling manual control of the associated clutch by manipulation of the associated control member upon lack of hydraulic power.

3. In a vehicle having drivable traction means; a friction steering clutch interposed in the drive to said traction means and having spring means for effecting engagement of the parts thereof; and hydraulic mechanism for controlling said steering clutch including a manually movable control member, a movable actuating member adapted to be moved by fluid pressure for effecting disengagement of said clutch against the action of said spring means, and a valve member movable to control application of fluid pressure on said actuating member and connected to said manually movable member so as to be moved thereby, said valve member and said actuating member having cooperating means rendering the extent of movement of said actuating member a function of the extent of movement of said valve member for enabling complete disengagement of said clutch or partial disengagement thereof whereby it may be slipped to render its action substantially the same as that obtainable by hand manipulation, and said valve memher being located between said manually movable control member and said actuating member to move said actuating member and thereby en able manual control of said clutch by manipulation of said manually movable control member upon lack of hydraulic power.

4. In a vehicle having drivable traction means at each side thereof; a friction steering clutch interposed in the drive to each of the traction means to enable steering of the vehicle by control thereof; and hydraulic mechanism for controlling the steering clutches independently or together including a manually manipulatable control member independently associated with each of the clutches, and hydraulic actuating means interposed between each of the control members and the clutch associated therewith, each of the actuating means embodying mechanism enabling complete disengagement of the associated clutch or partial disengagement thereof whereby the clutches may be slipped to render their action substantially the same as that obtainable by hand manipulation, and each of the actuating means also embodying mechanism enabling manual control of the associated clutch upon lack of hydraulic power.

5. A vehicle having drivable traction means at each side thereof; an engine for driving the traction means; releasable drive establishing means interposed in the drive to each of the traction means to enable steering of the vehicle by control thereof; and hydraulic mechanism for controlling the drive establishing means comprising a manually manipulatable control lever associated with each of the drive establishing means, and an axially movable connection including a plurality of axially alined parts movable in a straight line path between each of the control levers and the drive establishing means associated therewith enabling manual control of the associated drive establishing means by manipulation of the associated control lever upon lack of hydraulic power.

6. A track-type tractor having drivable endless track mechanism at each side thereof; an engine for driving such endless track mechanisms; a friction steering clutch interposed in the drive to each of the endless track mechanisms to enable steering of the tractor by control thereof; and hydraulic mechanism for controlling the steering clutches independently or together comprising a manually manipulatable control lever independently associated with each of the clutches, and an axially movable connection including a, plurality of axially alined parts movable in a straight line path and interposed between each of the control levers and the clutch associated therewith enabling manual control of the associated clutch by manipulation of the associated control lever upon lack of hydraulic power; one of the parts in each of said connections being a piston member adapted to be moved by fluid pressure for effecting disengagement of the associated clutch, and another of the parts being a valve member to control application of fluid pressure on the piston member, said piston member and said valve member in each connection having cooperating means rendering the extent of movement of the piston member a function of the extent of movement of the associated control lever for enabling complete disengagement of the associated clutch or partial disengagement thereof whereby the clutches may be slipped to render their action substantially the same as that obtainable by hand manipulation.

7. In a vehicle having drivable traction means at each side thereof; a friction steering clutch interposed in the drive to each of the traction means to enable steering of the vehicle by control thereof; brake mechanism associated with each of the traction means; and hydraulic mechanism for controlling the steering clutches independent of the control of the brake mechanisms including a plurality of independently manually manipulatable control members, one for each of the clutches, and hydraulic actuating means interposed between each of said control members and the clutch associated therewith, each of the actuating means embodying mechanism enabling complete disengagement of the associated clutch or partial disengagement thereof whereby the clutches may be slipped to render their action substantially the same as that obtainable by hand manipulation, and each of the actuating means also embodying mechanism enabling manual control of the associated clutch upon lack of hydraulic power.

8. In a vehicle having drivable traction means at each side thereof; an engine for driving said traction means; a friction steering clutch interposed in the drive to each of said traction means to enable steering of the vehicle by control thereof; liquid pressure operable hydraulic mechanism for controlling the steering clutches independently or together including a manually manipulatable control member independently associated with each of the clutches, and hydraulic actuating means interposed between each of such control members and the clutch associated therewith, each of the actuating means embodying mechanism enabling complete disengagement of the associated clutch or partial disengagement thereof, and also mechanism enabling manual control of the associated clutch upon lack of hydraulic power; and common pumping means for said actuating means driven from the engine for supplying liquid under pressure to said actuating means.

HARMON S. EBERI-IARD. GEORGE W. LEWIS. 

